Rivet analyses

title: CLEOII_1992_I32611

Charged particle multiplicity and 2nd Fox-Wolfram moment in $\chi^\prime_{b0,1,2}$ Decays

Experiment: CLEOII (CUSB)

Inspire ID: 32611

Status: UNVALIDATED

Authors: - Peter Richardson

References: - Phys.Rev. D46 (1992) 4822-4827

Beams: * *

Beam energies: ANY

Run details: - Any process producing chi_b(2P), original e+e-> Upsilon(3S)

Measurement of the average charged particle multiplicity, and the charged multiplicity distribution in $\chi^\prime_{b0,1,2}$ Decays. In addition the average 2nd Fox-Wolfram moment, and its distribution is also measured.

Source code:CLEOII_1992_I32611.cc

```c++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief chi_b(2S) decays class CLEOII_1992_I32611 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(CLEOII_1992_I32611);


/// @name Analysis methods
/// @{

/// Book histograms and initialise projections before the run
void init() {
  // Initialise and register projections
  declare(UnstableParticles(), "UFS");
  // Book histograms
  // averages
  book(_h_N_aver, 1, 1, 1);
  book(_h_R2_aver, 1, 1, 2);
  // dists
  _h_N = {Histo1DPtr(), Histo1DPtr(), Histo1DPtr()};
  _h_R2 = {Histo1DPtr(), Histo1DPtr(), Histo1DPtr()};
  book(_h_N[0], 2, 1, 1);
  book(_h_N[1], 2, 1, 2);
  book(_h_N[2], 2, 1, 3);
  book(_h_R2[0], 3, 1, 1);
  book(_h_R2[1], 3, 1, 2);
  book(_h_R2[2], 3, 1, 3);
}

void findDecayProducts(Particle parent, Particles& children, unsigned int& nCharged) {
  for (const Particle& p : parent.children()) {
    if (p.children().empty()) {
      if (isCharged(p)) ++nCharged;
      children.push_back(p);
    }
    else
      findDecayProducts(p, children, nCharged);
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  Particles chib = apply<UnstableParticles>(event, "UFS")
                       .particles(Cuts::pid == 110551 or Cuts::pid == 120553 or Cuts::pid == 100555);
  for (const Particle& p : chib) {
    unsigned int iHist = (p.pid() % 10) / 2;
    unsigned int nCharged(0);
    Particles children;
    findDecayProducts(p, children, nCharged);
    // ncharged
    _h_N[iHist]->fill(nCharged);
    _h_N_aver->fill(iHist, nCharged);
    // R_2
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
    vector<FourMomentum> mom;
    mom.reserve(children.size());
    for (const Particle& p2 : children) {
      mom.push_back(boost.transform(p2.momentum()));
    }
    // compute R2
    double H0(0.), H2(0.);
    for (const FourMomentum& p1 : mom) {
      double mod1 = p1.p3().mod();
      Vector3 axis = p1.p3().unit();
      for (const FourMomentum& p2 : mom) {
        double mod2 = p2.p3().mod();
        double cTheta = axis.dot(p2.p3().unit());
        H0 += mod1 * mod2;
        H2 += mod1 * mod2 * 0.5 * (3. * sqr(cTheta) - 1.);
      }
    }
    double R2 = H2 / H0;
    _h_R2[iHist]->fill(R2);
    _h_R2_aver->fill(iHist, R2);
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  for (unsigned int ix = 0; ix < 3; ++ix) {
    normalize(_h_N[ix]);
    normalize(_h_R2[ix]);
  }
}

/// @}


/// @name Histograms
/// @{
vector<Histo1DPtr> _h_N, _h_R2;
BinnedProfilePtr<int> _h_N_aver, _h_R2_aver;
/// @}

};

RIVET_DECLARE_PLUGIN(CLEOII_1992_I32611);

} ```